RFID antenna array for gaming

ABSTRACT

An RFID system includes multiple antennas and uses amplitude and phase information of the RFID signals received by each antenna to determine the position of RFID tags in the vicinity. More than one antenna can receive the RFID signals during a single read cycle, enabling the RFID system to operate more quickly than a system that energizes antennas separately.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/114,018 filed Aug. 27, 2018 for “RFID Antenna Array ForGaming”, which is a continuation of U.S. patent application Ser. No.15/814,170 filed Nov. 15, 2017 for “RFID Antenna Array For Gaming”, bothof which are incorporated herein by reference.

BACKGROUND

The present invention relates to gaming, and in particular, to a radiofrequency identification (RFID) system with an antenna array fordetecting the locations of RFID tags on a gaming table.

Unless otherwise indicated herein, the approaches described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Tracking the location of gaming tokens in real-time on a gaming tablehas the potential to revolutionize the gaming industry by providing cashmanagement and improved security. Tying this data to specific playersallows casinos to create accurate player profiles while simultaneouslyalleviating the pit boss of mundane tasks that take years of training tohone.

Traditional RFID systems have tried to address the gaming market withlimited success. In a typical RFID system, the excitation antennadefines a “working volume” within which the energy projected by theantenna is sufficient to power the RFID tag. This “working volume” isgenerally poorly defined with the only option to increase/decrease powerto adjust the read range. But doing so extends the read range in ALLdirections, introducing cross-talk errors when multiple antennas are inclose proximity. Existing products on the market suffer from multipleshortcomings. First, they are limited to discrete betting spots. Second,they are limited in the chip stack heights they can read. Third, theyhave very poor discrimination between adjacent betting spots. Fourth,they have higher than acceptable read errors. Fifth, they have slow readrates that miss important events (e.g., placement and removal of chips,etc.).

These shortcomings limit the available technology to games where thebetting spots are widely separated (e.g. a single “pot”), to detectinginitial bets only (not capturing transient events such as payouts), andidentifying counterfeit tokens only prior to their use on a table (notduring gameplay).

U.S. Application Pub. No. 2013/0233923 discusses a ferrite coretechnology. The ferrite core technology overcomes many of theabove-noted shortcomings, but does not address the need to trackmultiple separate bets placed by different bettors on a single largerbetting spot (such as when “back bettors” share a betting spot withseated bettors on traditional Baccarat “racetrack” layouts). Also neededis the ability to discriminate the location of very closely spaced bets(such as can be found on a roulette table).

U.S. Application Pub. No. 2017/0228630 discusses a solution involvingtwo intersecting antenna arrays. One array of horizontal antennasprovides one coordinate, and a second array of vertical antennasprovides a second coordinate. Signal strength information comparingadjacent antennas may then be used to interpolate a higher fidelity setof coordinates.

Although the approach of U.S. Application Pub. No. 2017/0228630 doeswork, it suffers from the simple fact that reading RFID tags takestime—and reading tags multiple times for purposes of interpolationmultiplies the required time such that capturing an accurate “snapshot”of transient events with large numbers of tags may not practical incertain gaming environments.

The typical RFID system addresses the question, “Who's there?” Theresponse is a series of unique item identifiers (e.g., serial numbers).As discussed above, the ferrite core technology discussed in U.S.Application Pub. No. 2013/0233923 is directed to addressing theadditional question “Where are you?” as a way to track individual bets.

U.S. Application Pub. No. 2016/0217645 discusses using a networkanalyzer device prior to an RFID read, thereby being able to direct theRFID reader to only those antennas with tags present. This describes aserial approach that eliminates the “overhead” of looking for tags usingan RFID reader where none are present, as using the network analyzerdevice takes less time than using the RFID reader.

Both U.S. Application Pub. No. 2013/0233923 and U.S. Application Pub.No. 2016/0217645 involve the placement of bets in specific areas (thebetting spots). RFID tags not placed in one of the defined areas willnot be read correctly. Neither of these disclosures addresses the needto detect bets placed anywhere on a larger bounded area. The additionaldisclosure of U.S. Application Pub. No. 2017/0228630 does addressplacing multiple bets within a larger bounded area. However, the systemdisclosed therein involved multiple RFID reads to define the coordinatesof each bet, which is a time consuming process.

All three of U.S. Application Pub. No. 2013/0233923, U.S. ApplicationPub. No. 2016/0217645 and U.S. Application Pub. No. 2017/0228630describe systems to identify and locate RFID tags by using signalstrength information as measured by the RFID reader to determineproximity to a specific antenna. U.S. Application Pub. No. 2013/0233923describes a system that increases the signal strength at the properantenna, which further improves accuracy.

SUMMARY

One issue with existing systems that use an array of antennas to locatea tag within the array is the time involved in energizing each antenna,in order to read the RFID tags in the vicinity of each antenna and thenrepeat this process for each subsequent antenna. There is a need for afaster method to accurately locate and track individual closely spacedbets that can be placed anywhere within a defined boundary on a gamingtable. There is a need for increased speed in a system that applies gamerules to calculate the amounts and positions of the original bets, andalso to correlate transient events such as payouts to winning bets.

Given the above, embodiments are directed toward using phase informationof the detected RFID signals in order to improve the operation of thesystem.

According to an embodiment, a system determines the locations of objectsin a gaming environment. The system includes a main antenna associatedwith an area on a gaming table, a first plurality of antennas orientedin a first direction and associated with the area on the gaming table, asecond plurality of antennas oriented in a second direction, a mainradio frequency identification (RFID) transmitter coupled to the mainantenna, a main RFID receiver coupled to the main antenna, a firstplurality of RFID receivers coupled to the first plurality of antennas,a second plurality of RFID receivers coupled to the second plurality ofantennas, and a controller that controls the main RFID transmitter togenerate an RFID inventory command. The second direction differs fromthe first direction, the second plurality of antennas overlaps the firstplurality of antennas, the first plurality of antennas and the secondplurality of antennas intersect at a plurality of locations within thearea, and each of a plurality of RFID tags in the area responds to theRFID inventory command according to an anti-collision process. Inresponse to the RFID inventory command, the main RFID receiver receivesa first plurality of responses from the plurality of RFID tags, thefirst plurality of RFID receivers receives a second plurality ofresponses from the plurality of RFID tags, and the second plurality ofRFID receivers receives a third plurality of responses from theplurality of RFID tags. The controller determines an identifier for eachof the plurality of RFID tags using at least one of the first pluralityof responses, the second plurality of responses, and the third pluralityof responses, and the controller determines a position of each of theplurality of RFID tags by correlating amplitude information and phaseinformation of the first plurality of responses, amplitude informationand phase information of the second plurality of responses, andamplitude information and phase information of the third plurality ofresponses.

For a particular RFID tag of the plurality of RFID tags, the controllermay simultaneously determine the identifier and the position of theparticular RFID tag.

The RFID inventory command may be a single RFID inventory command thatresults in the controller determining the identifiers and the positionsof all the plurality of RFID tags.

The first plurality of antennas and the second plurality of antennas maybe overlapping and intersecting to define the position of each of theplurality of RFID tags in two dimensions within the area. The firstplurality of antennas and the second plurality of antennas may intersectorthogonally and define the position of each of the plurality of RFIDtags in an x dimension and a y dimension within the area.

The first plurality of antennas and the second plurality of antennas maydefine the position of each of the plurality of RFID tags using polarcoordinates within the area.

The first plurality of antennas may be formed as a firstnon-overlapping, single layer, and the second plurality of antennas maybe formed as a second non-overlapping, single layer. The first pluralityof antennas may be formed as an overlapping, dual layer.

The controller may determine the position of each of the plurality ofRFID tags using interpolation of the amplitude information of the secondplurality of responses and the amplitude information of the thirdplurality of responses.

The controller may determine that a subset of the plurality of RFID tagsare grouped together when the position of each RFID tag of the subset iswithin a defined range of at least one other RFID tag of the subset.

The controller may determine that a first subset of the plurality ofRFID tags corresponds to a bet, and that a second subset of theplurality of RFID tags corresponds to a payout associated with the bet,according to the position of the first subset and the position of thesecond subset.

The controller may determine the identifier for each of the plurality ofRFID tags using at least one of the second plurality of responses andthe third plurality of responses.

The controller may use the first plurality of responses as referenceinformation to normalize the second plurality of responses and the thirdplurality of responses. The controller may use the amplitude informationof the first plurality of responses to normalize the amplitudeinformation of the second plurality of responses and the amplitudeinformation of the third plurality of responses.

The controller may use the phase information of the first plurality ofresponses to determine relative phase information for the secondplurality of responses and relative phase information for the thirdplurality of responses.

When a first set of the plurality of RFID tags are associated with afirst position, and when a second set of the plurality of RFID tags areassociated with a second position, the controller may determine that thefirst set and the second set are a group when the first position and thesecond position are within a threshold distance.

According to an embodiment, a system determines the locations of objectsin a gaming environment. The system includes a main antenna associatedwith an area on a gaming table, a first plurality of antennas orientedin a first direction and associated with the area on the gaming table, asecond plurality of antennas oriented in a second direction, a mainradio frequency identification (RFID) transmitter coupled to the mainantenna, a main RFID receiver coupled to the main antenna, a firstplurality of RFID receivers coupled to the first plurality of antennas,a second plurality of RFID receivers coupled to the second plurality ofantennas, and a controller that controls the main RFID transmitter togenerate an RFID inventory command. The second direction differs fromthe first direction, the second plurality of antennas overlaps the firstplurality of antennas, and the first plurality of antennas and thesecond plurality of antennas intersect at a plurality of locationswithin the area. Each of a plurality of RFID tags in the area respondsto the RFID inventory command according to an anti-collision process. Inresponse to the RFID inventory command, the main RFID receiver receivesa first plurality of responses from the plurality of RFID tags, thefirst plurality of RFID receivers receives a second plurality ofresponses from the plurality of RFID tags, and the second plurality ofRFID receivers receives a third plurality of responses from theplurality of RFID tags. The controller determines an identifier for eachof the plurality of RFID tags using at least one of the first pluralityof responses, the second plurality of responses, and the third pluralityof responses. The controller determines a position of each of theplurality of RFID tags by correlating amplitude information of the firstplurality of responses, amplitude information and phase information ofthe second plurality of responses, and amplitude information and phaseinformation of the third plurality of responses.

The details of this embodiment may otherwise be similar to the detailsof the previous embodiment.

According to an embodiment, a method determines the locations of objectsin a gaming environment. The method includes generating, by a main radiofrequency identification (RFID) transmitter coupled to a main antenna,an RFID inventory command, where the main antenna is associated with anarea on a gaming table. The method further includes responding, by eachof a plurality of RFID tags in the area, to the RFID inventory commandaccording to an anti-collision process. The method further includesreceiving, by a main RFID receiver coupled to the main antenna, a firstplurality of responses from the plurality of RFID tags in the area inresponse to the RFID inventory command. The method further includesreceiving, by a first plurality of RFID receivers coupled to a firstplurality of antennas, a second plurality responses from the pluralityof RFID tags in response to the RFID inventory command, where the firstplurality of antennas is oriented in a first direction and is associatedwith the area on the gaming table. The method further includesreceiving, by a second plurality of RFID receivers coupled to a secondplurality of antennas, a third plurality of responses from the pluralityof RFID tags in response to the RFID inventory command, where the secondplurality of antennas is oriented in a second direction that differsfrom the first direction, where the second plurality of antennasoverlaps the first plurality of antennas, and where the first pluralityof antennas and the second plurality of antennas intersect at aplurality of locations within the area. The method further includesdetermining, by a controller, an identifier for each of the plurality ofRFID tags using at least one of the first plurality of responses, thesecond plurality of responses, and the third plurality of responses. Themethod further includes determining, by the controller, a position ofeach of the plurality of RFID tags by correlating amplitude informationof the first plurality of responses, amplitude information and phaseinformation of the second plurality of responses, and amplitudeinformation and phase information of the third plurality of responses.

The step of determining the position of each of the plurality of RFIDtags may further include determining, by the controller, the position ofeach of the plurality of RFID tags by correlating the amplitudeinformation and phase information of the first plurality of responses,the amplitude information and phase information of the second pluralityof responses, and the amplitude information and phase information of thethird plurality of responses.

The details of this embodiment may otherwise be similar to the detailsof the previous embodiments.

According to an embodiment, a system determines the locations of objectsin a gaming environment. The system includes a main antenna associatedwith an area on a gaming table, a first plurality of antennas orientedin a first direction and associated with the area on the gaming table,and a second plurality of antennas oriented in a second direction, amain radio frequency identification (RFID) transmitter coupled to themain antenna, a first plurality of RFID receivers coupled to the firstplurality of antennas, a second plurality of RFID receivers coupled tothe second plurality of antennas, and a controller. The second directiondiffers from the first direction, the second plurality of antennasoverlaps the first plurality of antennas, and the first plurality ofantennas and the second plurality of antennas intersect at a pluralityof locations within the area. The controller controls the main RFIDtransmitter to generate an RFID inventory command, where each of aplurality of RFID tags in the area responds to the RFID inventorycommand according to an anti-collision process. In response to the RFIDinventory command, the first plurality of RFID receivers receives afirst plurality of responses from the plurality of RFID tags, and thesecond plurality of RFID receivers receives a second plurality ofresponses from the plurality of RFID tags. The controller determines anidentifier for each of the plurality of RFID tags using at least one ofthe first plurality of responses and the second plurality of responses.The controller determines a position of each of the plurality of RFIDtags by correlating amplitude information of the first plurality ofresponses, and amplitude information of the second plurality ofresponses.

The controller may determine the position of each of the plurality ofRFID tags by correlating the amplitude information and phase informationof the first plurality of responses, and the amplitude information andphase information of the second plurality of responses.

The details of this embodiment may otherwise be similar to the detailsof the previous embodiments.

According to an embodiment, a method determines the locations of objectsin a gaming environment. The method includes generating, by a main radiofrequency identification (RFID) transmitter coupled to a main antenna,an RFID inventory command, where the main antenna is associated with anarea on a gaming table. The method further includes responding, by eachof a plurality of RFID tags in the area, to the RFID inventory commandaccording to an anti-collision process. The method further includesreceiving, by a first plurality of RFID receivers coupled to a firstplurality of antennas, a first plurality responses from the plurality ofRFID tags in response to the RFID inventory command, where the firstplurality of antennas is oriented in a first direction and is associatedwith the area on the gaming table. The method further includesreceiving, by a second plurality of RFID receivers coupled to a secondplurality of antennas, a second plurality of responses from theplurality of RFID tags in response to the RFID inventory command, wherethe second plurality of antennas is oriented in a second direction thatdiffers from the first direction, where the second plurality of antennasoverlaps the first plurality of antennas, and where the first pluralityof antennas and the second plurality of antennas intersect at aplurality of locations within the area. The method further includesdetermining, by a controller, an identifier for each of the plurality ofRFID tags using at least one of the first plurality of responses, andthe second plurality of responses. The method further includesdetermining, by the controller, a position of each of the plurality ofRFID tags by correlating amplitude information of the first plurality ofresponses, and amplitude information of the second plurality ofresponses.

The step of determining the position of each of the plurality of RFIDtags may include determining, by the controller, the position of each ofthe plurality of RFID tags by correlating the amplitude information andphase information of the first plurality of responses, and the amplitudeinformation and phase information of the second plurality of responses.

The details of this embodiment may otherwise be similar to the detailsof the previous embodiments.

The following detailed description and accompanying drawings provide afurther understanding of the nature and advantages of embodiments of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an RFID system 100.

FIG. 2 is a flowchart of a method 200 of operating an RFID system (e.g.,the RFID system 100 of FIG. 1).

FIG. 3 is a graph showing a plot 300 of amplitude and phase informationdetected by one of the antennas 104 or 106 (see FIG. 1) as the chip ismoved across it.

FIG. 4 is a graph showing plots 400 and 402 of amplitude and phaseinformation detected by two of the antennas 104, or by two of theantennas 106 (see FIG. 1).

FIG. 5 is an overhead view of the antennas 104 and 106 of FIG. 1.

FIG. 6 is a block diagram of an RFID system 600. The RFID system 600shows a specific implementation of the RFID system 100 (see FIG. 1).

FIG. 7 is a block diagram of a receiver 700.

FIG. 8 is a block diagram of an RFID system 800.

FIG. 9 is an overhead view of a set of overlapping antennas 900 in onedirection.

FIG. 10 is an overhead view of an antenna array 1000.

FIG. 11 is an overhead view of a polar antenna array 1100.

FIG. 12A is an overhead view of a Baccarat table 1200, and FIG. 12B isan overhead view of a portion of the Baccarat table 1200 showing acorresponding portion of an antenna array 1202.

FIG. 13 is an overhead view of a roulette table 1300 having an antennaarray 1302.

FIG. 14 is an overhead view of the antennas 104 and 106 of FIG. 1

DETAILED DESCRIPTION

Described herein are techniques for location determination of RFID tags.In the following description, for purposes of explanation, numerousexamples and specific details are set forth in order to provide athorough understanding of the present invention. It will be evident,however, to one skilled in the art that the present invention as definedby the claims may include some or all of the features in these examplesalone or in combination with other features described below, and mayfurther include modifications and equivalents of the features andconcepts described herein.

In the following description, various methods, processes and proceduresare detailed. Although particular steps may be described in a certainorder, such order is mainly for convenience and clarity. A particularstep may be repeated more than once, may occur before or after othersteps (even if those steps are otherwise described in another order),and may occur in parallel with other steps. A second step is required tofollow a first step only when the first step must be completed beforethe second step is begun. Such a situation will be specifically pointedout when not clear from the context.

In this document, the terms “and”, “or” and “and/or” are used. Suchterms are to be read as having an inclusive meaning. For example, “A andB” may mean at least the following: “both A and B”, “at least both A andB”. As another example, “A or B” may mean at least the following: “atleast A”, “at least B”, “both A and B”, “at least both A and B”. Asanother example, “A and/or B” may mean at least the following: “A andB”, “A or B”. When an exclusive-or is intended, such will bespecifically noted (e.g., “either A or B”, “at most one of A and B”).

In this document, the terms “RFID tag”, “RFID gaming tag”, “RFID chip”,“RFID gaming chip”, “gaming chip”, and “gaming token” are used. Suchterms are to be read as being broadly synonymous. (More precisely, an“RFID chip” may be used to refer to the integrated circuit components ofthe “RFID tag”, which also includes additional components such as anantenna, a rigid housing, etc. However, this document is mostlyconcerned with the broad usage for these terms.) The RFID tag respondsto a radio frequency signal from the RFID reader, generally with itsserial number or other identifier, enabling the RFID reader to obtain aninventory of the RFID tags in the vicinity. In a gaming context, theRFID gaming tags may be placed on, removed from, or moved around on agaming table as bets and payouts, according to various game rules. TheRFID gaming tags may be marked with a value identifier (e.g., $1).

FIG. 1 is a block diagram of an RFID system 100. The RFID system 100includes a main antenna 102, a first set of antennas 104 a-104 d(collectively antennas 104), a second set of antennas 106 a-106 d(collectively antennas 106), a main RFID transmitter 108, a main RFIDreceiver 112, a first set of RFID receivers 114 a-114 d (collectivelyRFID receivers 114), a second set of RFID receivers 116 a-116 d(collectively RFID receivers 116), and a controller 120. In general, themain RFID transmitter 108 generates radio frequency energy that isradiated by the antenna 102 and received by any RFID tags; the responsesfrom the RFID tags are then received by the antennas 102, 104 and 106.The responses from the RFID tags may be amplitude and phase information.The amplitude information may be in the form of received signal strength(RSSI) information, and the phase information may be in the form ofin-phase (I) and quadrature (Q) information.

The RFID system 100 may be implemented as part of a gaming table (see,e.g., the roulette and Baccarat examples of FIGS. 12A-12B and 13). Forexample, the antennas 102, 104 and 106 may be embedded below the playingsurface of the gaming table (in order to detect the locations of theRFID gaming tags during play on the gaming table), and the rest of thecomponents of the RFID system 100 may be embedded within the structureof the gaming table. The gaming environment may have a number of gamingtables, each including an RFID system 100; the multiple RFID systems 100may be connected to each other or to other components via a network.

The main antenna 102 is located under the playing surface of the gamingtable. As part of playing games using the gaming table, RFID gaming tagsare placed on, removed from, and moved around on the area above the mainantenna 102. This area on the gaming table may be marked to show varioussubareas according to the particular game being implemented (see, e.g.,the roulette and Baccarat examples of FIGS. 12A-12B and 13). The mainantenna 102 may be implemented on a printed circuit board. The main RFIDtransmitter 108 and the main receiver 112 are coupled to the mainantenna 102.

The antennas 104 are located under the playing surface of the gamingtable and, like the main antenna 102, are associated with the gameplayarea. The antennas 104 are oriented in a first direction. As shown inFIG. 1, the antennas 104 are oriented in the north-south (or y)direction. In other implementations, the antennas 104 may be oriented inother directions. The antennas 104 may be implemented on a printedcircuit board, or as a layer of a multilayer circuit board that alsoincludes the main antenna 102. The RFID receivers 114 are coupled to theantennas 104.

The antennas 106 are located under the playing surface of the gamingtable and, like the main antenna 102, are associated with the gameplayarea. The antennas 106 are oriented in a second direction that differsfrom the first direction of the antennas 104. As shown in FIG. 1, theantennas 106 are oriented in the east-west (or x) direction. In otherimplementations, the antennas 106 may be oriented in other directions.The antennas 106 may be implemented on a printed circuit board, or as alayer of a multilayer circuit board that also includes the main antenna102 or the antennas 104. The RFID receivers 116 are coupled to theantennas 106.

The antennas 106 overlap the antennas 104; this overlap is shown usingdotted lines in FIG. 1. This overlap generally allows both the antennas104 and 106 to be associated with the gameplay area, in addition to themain antenna 102. In general, this allows at least three antennas (e.g.,the main antenna 102, one of the antennas 104, and one of the antennas106) to be associated with each location within the gameplay area. Thespacing between each of the antennas 104, and the spacing between eachof the antennas 106, may be adjusted as desired.

Collectively, the antennas 104 and 106 form what may be referred to asan antenna array. As shown in FIG. 1, the antennas 104 and 106 intersectat right angles. In other implementations, the antennas 104 and 106 mayintersect at other angles. As shown in FIG. 1, the antennas 104 and 106are rectangular in shape. In other implementations, the antennas 104 mayhave other shapes, such as ring shapes, pie shapes, curved shapes,rounded rectangular shapes, etc. The sizes of the antennas 104 and 106may be adjusted as desired.

Four antennas 104 and four associated RFID receivers 114, and fourantennas 106 and four associated RFID receivers 116, are shown inFIG. 1. These quantities may be adjusted as desired to cover larger orsmaller areas and/or to increase or decrease spatial resolution.

In general, the main RFID receiver 112 is used to generate referenceamplitude and phase information that the controller 120 uses whenprocessing the amplitude and phase information from the antennas 104 and106. Although the main RFID receiver 112 is shown as a separatecomponent in FIG. 1, the main RFID receiver 112 may be a subcomponent ofthe main RFID transmitter 108.

The controller 120 generally controls the operation of the RFID system100. The controller 120 may be connected to, or may be a component of, acomputer (e.g., a personal computer). The controller 120 may connect toother components, or may itself include components, that implement otherfunctions such as RFID tag identification, RFID tag locationdetermination, game rules verification, etc. The controller 120 mayaccess various data stores or databases such as a game rules database,an RFID tag database, etc.

The RFID system 100 generally operates as follows. The transmitter 108generates a radio frequency signal that is transmitted by the mainantenna 102. Any RFID gaming tags in the gameplay area respond to theradio frequency signal. The responses from the RFID gaming tags arereceived by the main receiver 112 (via the main antenna 102), at leastone of the receivers 114 (via at least one of the antennas 104), and atleast one of the receivers 116 (via at least one of the antennas 106).The controller 120 determines the position of each RFID gaming tag bycorrelating the responses received by each of the receivers. Moredetails are provided with reference to FIG. 2.

According to another embodiment, the main receiver 112 may be omitted.

FIG. 2 is a flowchart of a method 200 of operating an RFID system (e.g.,the RFID system 100 of FIG. 1). The method 200 may be controlled by acontroller (e.g., the controller 120 of FIG. 1), for example, accordingto the execution of a computer program. In general, the method 200describes a single RFID read cycle. Between read cycles, the RFID gamingtags are unpowered and do not send signals. During the RFID read cycle,each RFID gaming tag in the gameplay area responds. The RFID read cycleends after each RFID gaming tag has responded. Thus, each RFID readcycle results in all the RFID gaming tags in the gameplay respondingonce but being read by multiple receivers.

At 202, the controller controls a main RFID transmitter (e.g., the mainRFID transmitter 108 of FIG. 1) to generate an RFID inventory command.In general, the main RFID antenna is energized, and the RFID inventorycommand is one of a number of commands that may be included in the radiofrequency energy generated by the main RFID transmitter. Further detailsof the RFID inventory command are provided below. A main antenna (e.g.,the main antenna 102 of FIG. 1) coupled to the main RFID transmittertransmits the RFID inventory command. The main antenna is associatedwith an area on a gaming table that contains one or more RFID tags(e.g., RFID gaming tags).

At 204, each of the RFID tags responds to the RFID inventory commandaccording to an anti-collision process. In general, the anti-collisionprocess helps ensure that only one of the RFID tags is responding at agiven time. Further details of the anti-collision process are providedbelow.

At 206, a main RFID receiver (e.g., the main RFID receiver 112 ofFIG. 1) coupled to the main antenna receives a first set of responsesfrom the RFID tags in the area in response to the RFID inventorycommand.

At 208, a first set of RFID receivers (e.g., the RFID receivers 114 ofFIG. 1) coupled to a first set of antennas (e.g., the antennas 104 ofFIG. 1) receives a second set of responses from the RFID tags in thearea in response to the RFID inventory command. The first set ofantennas is oriented in a first direction and is associated with thearea on the gaming table.

At 210, a second set of RFID receivers (e.g., the RFID receivers 116 ofFIG. 1) coupled to a second set of antennas (e.g., the antennas 106 ofFIG. 1) receives a third set of responses from the RFID tags in the areain response to the RFID inventory command. The second set of antennas isoriented in a second direction that differs from the first direction,the second set of antennas overlaps the first set of antennas, and thefirst set of antennas and the second set of antennas intersect at anumber of locations within the area.

As mentioned above, each RFID tag responds once, but each response isreceived by multiple antennas. For ease of description, these receivedresponses are referred to as the “first set of responses”, the “secondset of responses” and the “third set of responses” in 206-210 above. Ingeneral, each of the multiple antennas receives a particular responsesimultaneously.

Due to the anti-collision process, ideally only one of the RFID tags isresponding at a given time, so controller is able to associate theresponses received by each of the antennas at that given time with thatone responding RFID tag. So generally 206-210 occur in parallel, witheach RFID tag (ideally) responding at a given time and being detected bymultiple receivers. For example, at a given time, the response from oneRFID tag is received by the main RFID receiver, at least one of thefirst set of RFID receivers, and at least one of the second set of RFIDreceivers.

A brief description of the anti-collision process is as follows. Thecontroller puts out a start of inventory command which includes a 5 bitcyclic redundancy check (CRC). This command also defines how many slotsthere are. The tag creates a random number and compares it to theparticular slot number. If it matches then the tag responds with the 5bit CRC from the command along with the 16 bit CRC of its serial number.If the controller receives this without detecting a collision then itresends the 5 bit CRC and the 16 bit CRC to the tags. The tag thenresponds by sending out its serial number and sets its flag so it doesnot respond to more queries until the flag is reset when RF power isremoved. Thus, sending the CRC before the actual data speeds things asit is a shorter message to determine if there is a collision.

At 212, a controller (e.g., the controller 120 of FIG. 1) determines anidentifier for each of the RFID tags using at least one of the first setof responses, the second set of responses, and the third set ofresponses. As discussed above, when a given tag responds with its serialnumber according to the anti-collision process, this response may bereceived by multiple RFID receivers (e.g., the main RFID receiverreceives the first set of responses, including the response from thegiven tag; the first set of RFID receivers receives the second set ofresponses, including the response from the given tag; etc.). Thecontroller may use one of the RFID receivers (e.g., the main RFIDreceiver) to determine the identifiers, and may use the information fromthe other RFID receivers for verification or confirmation purposes. Whenthe current read cycle ends, the RFID tag loses power, the flag iscleared, and that RFID tag is free to respond during the next readcycle.

At 214, the controller determines a position of each of the RFID tags bycorrelating amplitude and phase information of the first set ofresponses with amplitude and phase information of the second set ofresponses and amplitude and phase information of the third set ofresponses. Further details of this correlation process are providedbelow. In general, the controller uses the information from the firstset of responses to modify the second set of responses in order todetermine one dimension of the position (e.g., the x dimension), anduses the information from the first set of responses to modify the thirdset of responses in order to determine another dimension of the position(e.g., the y dimension); the intersection of the x dimension and the ydimension then indicates the position of the RFID tag in the gamingarea.

As an alternative in 214, the controller may determine a position ofeach of the RFID tags by correlating amplitude information only (notphase information) of the first set of responses with amplitude andphase information of the second set of responses and amplitude and phaseinformation of the third set of responses. In this alternative, the mainRFID receiver just performs excitation, and its amplitude information isused for normalization purposes; the phase information from the firstand second sets of antennas is used to determine the position.

As another alternative in 214, the controller may determine a positionof each of the RFID tags by correlating amplitude information of thefirst set of responses with amplitude information of the second set ofresponses and amplitude information of the third set of responses.

The controller may perform 212-214 in parallel, or may perform 214 priorto 212.

Once all of the RFID tags have responded, the current read cycle iscomplete. When the controller performs the next read cycle, thecontroller performs the method 200 again.

The controller may then use the identifier and position of each of theRFID tags to perform other gaming functions such as verifying theamounts and placements of bets and payouts, verifying conformance of theRFID tag placements with various game rules, etc. Further details ofthese gaming functions are provided below.

As discussed above with reference to FIG. 1, an alternative embodimentomits the main RFID receiver. In such an embodiment, the controllerdetermines the identifier (see 212) and the position (see 214) withoutusing the first set of responses.

FIG. 3 is a graph showing a plot 300 of amplitude and phase informationdetected by one of the antennas 104 or 106 (see FIG. 1) as the chip ismoved across it. The plot 300 represents the amplitude and phaseinformation resulting from the response of a single RFID tag at eachgiven x position. For visualization purposes, imagine that we are usingthe antenna 104 a (see FIG. 1) to detect the RFID tag at each position.In FIG. 3, the antenna 104 a has a width of approximately 2 inches,positioned between approximately 1.8 and 3.8 inches from the zeroposition 302. So imagine that the RFID tag starts at the zero position302. This is outside the antenna 104 a and has a zero amplitude,corresponding to the RFID tag not being detected. The left side of theantenna 104 a begins at 304. As the RFID tag moves from 302 to 304, theantenna 104 a detects the amplitude of the response from the RFID tag,which increases as the RFID tag nears the antenna 104 a. (The amplitudeshown in FIG. 3 is normalized using the response received by the mainantenna 102 of FIG. 1.) Note that the amplitude of the plot 300 isnegative between 302 and 304; this is due to the comparison of the phaseinformation for the RFID tag detected by the main antenna 102 versus theantenna 104 a. Specifically, the phase information detected by the mainantenna 102 is out-of-phase with the phase information detected by thisantenna 104 a; this out-of-phase result is shown as the negativeamplitude in FIG. 3. The negative phase information indicates that theRFID tag is detected outside of the antenna 104 a.

When the RFID tag reaches 304 (directly above the left-side loop of theantenna 104 a), the amplitude information is zero, corresponding to theRFID tag not being detected. As the RFID tag moves toward the center ofthe antenna 104 a, the amplitude increases, reaching a maximum of about0.75 at 306. Since the phase information detected by the main antenna102 is in-phase with the phase information detected by the antenna 104a, this indicates that the RFID tag is inside both antennas, and isshown by the positive amplitude curve of the plot 300 between 304 and308. As the RFID tag moves toward the right-side loop of the antenna 104a, the amplitude decreases down to zero at 308.

As the RFID tag continues past 308, the antenna 104 a detects that theamplitude information increases (negatively) for a bit before returningto zero at 310. As before, the amplitude is shown as a negative valuedue to the phase information comparison between the main antenna 102 andthe antenna 104 a. Since the RFID tag is inside the main antenna 102 butoutside the antenna 104 a between 308 and 310, the comparison result isout-of-phase, and the amplitude of the plot 300 is shown as a negativebetween 308 and 310.

As an example, imagine that the antenna 104 a detects an amplitude of0.2. Using just the amplitude information, the RFID tag could be at theposition corresponding to one of six points: 320, 322, 324, 326, 330 or332. If the phase information indicates out-of-phase, the RFID tag couldbe at the position corresponding to one of the four points 320, 322, 324or 326. If the phase information indicates in-phase, the RFID tag couldbe at the position corresponding to one of the two points 330 or 332.Next, FIG. 4 shows how adjacent antennas can be used to narrow thesemultiple positions down to a single position.

FIG. 4 is a graph showing plots 400 and 402 of amplitude and phaseinformation detected by two of the antennas 104, or by two of theantennas 106 (see FIG. 1). For illustrative purposes, assume that theplot 400 corresponds to the signal received by the antenna 104 a,similar to the plot 300 (see FIG. 3); the plot 402 corresponds to thesignal received by the nearby antenna 104 b. The antennas 104 a and 104b may be referred to as adjacent antennas. The plots 400 and 402 areotherwise similar to the plot 300 (see FIG. 3).

Due to the distance between the antennas 104 a and 104 b, there is someoverlap among the plots 400 and 402. This overlap provides the RFIDsystem 100 (see FIG. 1) with the ability to correlate the amplitude andphase information detected by each antenna with the position of the RFIDtag.

Returning to the example discussed above regarding FIG. 3, imagine thatthe antenna 104 a detects an in-phase amplitude of 0.2, which indicatesthe RFID tag could be at the position corresponding to one of twopoints: 430 or 432. Imagine that the antenna 104 b detects anout-of-phase amplitude of 0.2, which indicates that the RFID tag couldbe at the position corresponding to one of four points: 450, 452, 454 or456. By correlating these measurements, the RFID system 100 determinesthat the position of the RFID tag is the one that corresponds to point432 (antenna 104 a) and point 450 (antenna 104 b); on the gaming table,this position is slightly inside the right-hand side of the antenna 104a. (Note that FIG. 4 corresponds to a side view of the antenna 104 a, soin the overhead view of FIG. 1, the position of the RFID tag correspondsto one on a line slightly inside the right-hand side of the antenna 104a.) Next, FIG. 5 shows how to extend this example to two dimensions.

FIG. 5 is an overhead view of the antennas 104 and 106 of FIG. 1.Continuing the thought experiment discussed above regarding FIG. 4,imagine that the RFID system 100 uses the antennas 104 to determine thatthe RFID tag is on a position corresponding to the line 502, due to theamplitude and phase information detected by the antennas 104 a and 104b. Further imagine that the RFID system 100 uses the antennas 106 todetermine that the RFID tag is on a position corresponding to the line504, due to the amplitude and phase information detected by the antennas106 a and 106 b (in a manner similar to that discussed above regardingthe antennas 104 a and 104 b). The RFID system 100 is then able todetermine the position of the RFID tag as the intersection of the lines502 and 504, position 506. In this manner, the RFID system 100 is ableto determine the positions of one or more RFID tags in the vicinity ofthe antenna array.

FIG. 6 is a block diagram of an RFID system 600. The RFID system 600shows a specific implementation of the RFID system 100 (see FIG. 1). TheRFID system 600 includes a main antenna 602, a first set of antennas 604a-604 d (collectively antennas 604), a second set of antennas 606 a-606d (collectively antennas 606), an RFID reader 608, a main RFID receiver612, a first set of RFID receivers 614 a-614 d (collectively RFIDreceivers 614), a second set of RFID receivers 616 a-616 d (collectivelyRFID receivers 616), and controllers 620 a and 620 b (collectivelycontrollers 620). These components are similar to the componentsdiscussed above regarding the RFID system 100 (see FIG. 1). The RFIDsystem 600 also includes an oscillator 630, a signal divider 632,microprocessors 640 a-640 i (collectively microprocessors 640), adual-directional coupler 650, and a diode detector 652.

The RFID reader 608 includes an RFID transmitter and a RFID receiver.The RFID transmitter is similar to the main RFID transmitter 108 (seeFIG. 1). The RFID receiver enables the RFID reader 608 to read theidentifiers of the RFID tags, if so desired. The RFID reader 608 may bea “stock” or “off the shelf” RFID reader. The RFID reader 608 generatesa radio frequency signal that is provided to the dual directionalcoupler 650. The RFID reader 608 may also read the identifiers of theresponses from any RFID tags in the area.

The oscillator 630 generates a first local oscillator signal at adesired frequency. For the RFID system 600, the RFID tags are designedto operate at a frequency of 13.56 MHz. This frequency may be adjustedas desired in other embodiments. The oscillator 630 provides this firstlocal oscillator signal to the receivers 612, 614 and 616 (as also shownin FIG. 7), and to the signal divider 632.

The signal divider 632 divides the first local oscillator signal fromthe oscillator 630 in order to generate a second local oscillatorsignal. For the RFID system 600, the RFID tags are designed to operatewith a modulation frequency of 424 kHz. Thus, the signal divider 632divides the 13.56 MHz signal by 32 to get 424 kHz. The modulationfrequency may be adjusted as desired in other embodiments. The signaldivider 632 provides this second local oscillator signal to thereceivers 612, 614 and 616 (as also shown in FIG. 7).

The microprocessors 640 process the amplitude and phase information fromthe receivers 612, 614 and 616, and provide the amplitude and phaseinformation from each of the receivers to the controller 620 b. Themicroprocessors 640 receive an enable signal from the controller 620 bto selectively enable them.

The dual-directional coupler 650 generally couples the RFID reader 608,the main antenna 602, the main RFID receiver 612, and the controller 620b (via the diode detector 652). The dual-directional coupler 650 couplesthe radio frequency energy transmitted by the RFID reader 608 to themain antenna 602, and directs a portion of the transmitted radiofrequency energy to the controller 620 b (via the diode detector 652).The dual-directional coupler 650 couples the radio frequency energyreceived by the main antenna 602 to the RFID reader 608, and directs aportion of the received radio frequency energy to the main RFID receiver612.

The diode detector 652 generally functions as an envelope detector. Thecontroller 620 b uses the output of the diode detector to determine thetime at which a tag may be responding. This allows the controller 620 bto have the receivers 614 and 616 start sampling the antenna signals.

The controllers 620 generally control the operation of the RFID system600, as discussed above regarding the controller 120 (see FIG. 1) andthe method 200 (see FIG. 2). The controller 620 a generally controls theRFID reader 608, and processes the data collected by the controller 620b in order to determine the positions of the RFID tags. The controller620 a may connect to the RFID reader 608 via an Ethernet connection, andmay connect to the controller 620 b via a universal serial bus (USB)connection. The controller 620 a may be implemented with a computer(e.g., a personal computer) that is connected via a network to otherdevices. The controller 620 b generally collects the amplitude and phaseinformation received by the receivers 612, 614 and 616. The controller620 b may be implemented with a microprocessor or a programmable logicdevice.

The RFID system 600 generally operates as follows. The controller 620 ainstructs the RFID reader 608 to transmit an inventory command. The RFIDreader 608 turns on its radio frequency output and sends a signal to theRFID tags (e.g., by amplitude modulating the carrier signal of its radiofrequency output). The dual-directional coupler 650 directs a portion ofthis signal to the diode detector 652. The controller 620 b monitors theoutput of the diode detector 652 in order to determine when to have thereceivers start sampling for an RFID tag which may be responding to theRFID reader 608. At this time, the controller 620 b instructs themicroprocessors 640, using the enable signal, to begin sampling the RSSIinformation. When the controller 620 b determines the end of the RFIDtag response, the controller 620 b uses the enable signal to instructthe microprocessors 640 to sample the I and Q levels from the receivers612, 614 and 616, and to process the RSSI information to determine thedata returned by the RFID tag. (This data is generally the serial numberof the RFID tag, in response to the inventory command.) The I and Qinformation determine the phase of the modulated second local oscillatorsignal of the response from the RFID tag (e.g., at 424 kHz). Note thatthe phase of the modulated second local oscillator signal isindeterminate when using a single one of the receivers 614 or 616.However, by comparing the phase detected by one of the receivers 614 or616 and the phase detected by the receiver 612, the controller 620 b isable to determine whether or not the RFID tag is inside of, or outsideof, a given antenna loop.

The oscillator 630 provides the first local oscillator signal (e.g.,13.56 MHz) to the receivers 612, 614 and 616, and to the signal divider632. The signal divider 632 generates the second local oscillator signal(e.g., 424 kHz) and provides this second local oscillator signal to thereceivers 612, 614 and 616. The RFID tags respond to the inventorycommand by load modulating a subcarrier signal onto the carrier signaltransmitted by the RFID reader 608. The receivers 612, 614 and 616determine the modulated subcarrier signal from the RFID tags by firstmixing the antenna signal first with the first local oscillator signal.After filtering and amplifying, the signal is mixed with the secondlocal oscillator signal to demodulate the modulated subcarrier signal tobaseband to determine the I and Q components.

The controller 620 b analyzes the data from the receivers 614, and thedata from the receiver 612, to determine the location of the RFID tag onthe x axis. Similarly, the controller 620 b analyzes the data from thereceivers 616, and the data from the receiver 612, to determine thelocation of the RFID tag on the y axis. The controller 620 b may use theRSSI from the receiver 612 to normalize the signals received from theother receivers 614 and 616 so that higher fidelity position informationcan be attained.

Although four sets of antennas 604 and antennas 606 (and theirassociated receivers 614 and 616) are shown, these numbers may beadjusted as desired. Similarly, the shapes of the antennas 604 and 606may be adjusted.

FIG. 7 is a block diagram of a receiver 700. The receiver 700 may be aspecific implementation for one or more of the receivers 612, 614 or 616(see FIG. 6). The receiver 700 includes a mixer 702, a band-pass filter704, an amplifier 706, a band-pass filter 708, a limiting amplifier 710,mixers 712 a and 712 b, a phase shifter 714, resistors 716 a and 716 b,and capacitors 718 a and 718 b.

The receiver 700 is connected to one of the antennas (e.g., one of theantennas 602, 604 or 606 of FIG. 6). The receiver 700 receives a firstlocal oscillator (LO) signal 730 (e.g., at 13.56 MHz) from theoscillator 630 (see FIG. 6), and receives a second local oscillatorsignal 732 (e.g., at 424 kHz) from the signal divider 632 (see FIG. 6).

The mixer 702 mixes the radio frequency signal received by the antenna(e.g., one of the antennas 602, 604 or 606 of FIG. 6) with the firstlocal oscillator signal 730, in order to generate a modulated subcarriersignal 734 (e.g., at 424 kHz). (The subcarrier signal 734 is a modulatedsubcarrier signal due to the radio frequency energy from the RFID reader(e.g., 608 in FIG. 6) being modulated by the RFID tag in the area.)

The band-pass filter 704 performs band-pass filtering on the modulatedsubcarrier signal 734 to reduce the noise, and generates a modulatedsubcarrier signal 736. The band-pass filter 704 has a center frequencyaround the expected frequency of the subcarrier signal (e.g., 424 kHz).

The amplifier 706 amplifies the modulated subcarrier signal 736, andgenerates a modulated subcarrier signal 738. The band-pass filter 708performs band-pass filtering on the modulated subcarrier signal 738 tofurther reduce the noise, and generates a modulated subcarrier signal740. The band-pass filter 708 has a center frequency around the expectedfrequency of the subcarrier signal (e.g., 424 kHz).

The limiting amplifier 710 drives the modulated subcarrier signal 740into limiting (e.g., by having a high gain) so that the I and Q phasesignals are independent of signal amplitude, resulting in a modulatedsubcarrier signal 742. The limiting amplifier 710 also outputs a RSSIsignal 744 that is proportional to the level of the modulated subcarriersignal 740 (e.g., in dB). The RSSI signal 744 is then provided to thecontroller 620 b of FIG. 6, and corresponds to the RSSI or amplitudeinformation discussed above.

The mixer 712 a mixes the modulated subcarrier signal 742 with thesecond local oscillator signal 732 in order to extract a modulatedsignal 746. The modulated signal 746 corresponds to the modulation ofthe subcarrier signal (e.g., at 424 kHz) performed by the RFID tag inthe area. The resistor 716 a and the capacitor 718 a form a low-passfilter that performs low-pass filtering on the modulated signal 746,resulting in an in-phase (I) signal 748. The in-phase signal 748 is thenprovided to the controller 620 b of FIG. 6, and corresponds to thein-phase (I) signal component discussed above.

The phase shifter 714 performs phase-shifting by 90 degrees on thesecond local oscillator signal 732 to generates a phase-shifted secondlocal oscillator signal 733.

The mixer 712 b mixes the modulated subcarrier signal 742 with thephase-shifted second local oscillator signal 733 in order to create ademodulated signal 750. The demodulated signal 750 corresponds to anunfiltered quadrature (Q) signal. The resistor 716 b and the capacitor718 b form a low-pass filter that performs low-pass filtering on thedemodulated signal 750, resulting in a quadrature (Q) signal 752. Thequadrature signal 752 is then provided to the controller 620 b of FIG.6, and corresponds to the quadrature (Q) signal component discussedabove.

As discussed above, the controllers 620 (see FIG. 6) are able todetermine whether a given RFID tags is inside of, or outside of, one ormore of the antennas 604 and 606 by comparing the I and Q componentsreceived by that antenna with the I and Q components received by themain antenna 602.

According to another embodiment, instead of the receiver 700, thereceiver may be implemented as a software defined radio. In general, asoftware defined radio samples the signal from the antenna with a highspeed analog to digital converter, then processes the signals digitally,in order to detect the amplitude and phase.

FIG. 8 is a block diagram of an RFID system 800. The RFID system 800shows a specific implementation of the RFID system 100 (see FIG. 1). TheRFID system 800 includes a main antenna 802, a first set of antennas 804a-804 d (collectively antennas 804), a second set of antennas 806 a-806d (collectively antennas 806), an RF transmitter 808, a main RFIDreceiver 812, a first set of RFID receivers 814 a-814 d (collectivelyRFID receivers 814), a second set of RFID receivers 816 a-816 d(collectively RFID receivers 816), controllers 820 a and 820 b(collectively controllers 820), an oscillator 830, and a signal divider832. These components are similar to the components discussed aboveregarding the RFID system 100 (see FIG. 1) or the RFID system 600 (seeFIG. 6). The RFID system 800 also includes a directional coupler 850.

The RFID system 800 is similar to the RFID system 600 (see FIG. 6), withthe main differences being replacing the RFID reader 608 (see FIG. 6)with the RF transmitter 808, replacing the controller 620 b with thecontroller 820 b, and replacing the dual-directional coupler 650 withthe directional coupler 850. In brief, the RFID system 600 (see FIG. 6)is directed to using a “stock” or “off the shelf” RFID reader (the RFIDreader 608), and the RFID system 800 is directed to using a controllableRF transmitter (the RF transmitter 808).

The oscillator 830 generates a first local oscillator signal at adesired frequency. For the RFID system 800, the RFID tags are designedto operate at a frequency of 13.56 MHz. This frequency may be adjustedas desired in other embodiments. The oscillator 830 provides the firstlocal oscillator signal to the receivers 812, 814 and 816. The receivers812, 814 and 816 may be implemented in a manner similar to the receiver700 (see FIG. 7), in which case this signal corresponds to the firstlocal oscillator signal 730.

The signal divider 832 divides the first local oscillator signal fromthe oscillator 830 in order to generate a second local oscillatorsignal. For the RFID system 800, the RFID tags are designed to operatewith a modulation frequency of 424 kHz. Thus, the signal divider 832divides the 13.56 MHz signal by 32 to get 424 kHz. The modulationfrequency may be adjusted as desired in other embodiments. The signaldivider 832 provides this second local oscillator signal to thereceivers 812, 814 and 816 (as also shown in FIG. 7), in which case thissignal corresponds to the second local oscillator signal 732.

The directional coupler 850 generally couples the RF transmitter 808,the main antenna 802 and the main RFID receiver 812. The directionalcoupler 850 couples the radio frequency energy transmitted by the RFtransmitter 808 to the main antenna 802. The directional coupler 850couples the radio frequency energy received by the main antenna 802 tothe RF transmitter 808, and directs the received radio frequency energyto the main RFID receiver 812.

The controllers 820 generally control the operation of the RFID system800, as discussed above regarding the controller 120 (see FIG. 1) andthe method 200 (see FIG. 2). The controller 820 a generally acts as aninterface to the other components. The controller 820 a may connect tothe controller 820 b via an Ethernet connection. The controller 820 amay be implemented with a computer (e.g., a personal computer) that isconnected via a network to other devices. The controller 820 b generallycontrols the RF transmitter 808, collects the amplitude and phaseinformation received by the receivers 812, 814 and 816, and processesthe amplitude and phase information to determine the positions of theRFID tags. The controller 820 b may be implemented with a microprocessoror a programmable logic device.

The RFID system 800 generally operates as follows. The controller 820 bcontrols the RF transmitter 808 using a modulation signal 860. The RFtransmitter 808 applies the modulation signal 860 to its RF carriersignal to command the tags (e.g., to transmit an inventory command usingamplitude modulation of a subcarrier signal on the carrier signal of itsradio frequency output). The directional coupler 850 directs this signalto the main antenna 802. The controller 820 b receives the amplitude andphase information (RSSI, I and Q) from the receivers 812, 814 and 816.(This data is generally the serial number of the RFID tag, in responseto the inventory command.) The I and Q information determine the phaseof the modulated subcarrier of the response from the RFID tag (e.g., at424 kHz). Note that the phase of the modulated subcarrier isindeterminate when using a single one of the receivers 814 or 816.However, by comparing the phase detected by one of the receivers 814 or816 and the phase detected by the receiver 812, the controller 820 b isable to determine whether or not the RFID tag is inside of, or outsideof, a given antenna loop.

The oscillator 830 provides the first local oscillator signal (e.g.,13.56 MHz) to the receivers 812, 814 and 816, and to the signal divider832. The signal divider 832 generates the second local oscillator signal(e.g., 424 kHz) and provides this signal to the receivers 812, 814 and816. The RFID tags respond to the inventory command by load modulating asubcarrier signal onto the carrier signal transmitted by the RFtransmitter 808. The receivers 812, 814 and 816 determine the modulatedsubcarrier signal from the RFID tags by mixing the detected subcarriersignal with the first local oscillator signal from the oscillator 830.The receivers 812, 814 and 816 demodulate the modulated subcarriersignal to baseband to determine the I and Q components.

The controller 820 b analyzes the data from the receivers 814, and thedata from the receiver 812, to determine the location of the RFID tag onthe x axis. Similarly, the controller 820 b analyzes the data from thereceivers 816, and the data from the receiver 812, to determine thelocation of the RFID tag on the y axis. The controller 820 b may use theRSSI from the receiver 812 to normalize the signals received from theother receivers 814 and 816 so that higher fidelity position informationcan be attained.

Although four sets of antennas 804 and antennas 806 (and theirassociated receivers 814 and 816) are shown, these numbers may beadjusted as desired. Similarly, the shapes of the antennas 804 and 806may be adjusted.

FIG. 9 is an overhead view of a set of overlapping antennas 900 in onedirection. The overlapping of the antennas 900 increases the number ofantennas that may receive the response from a given RFID tag, whichincreases the amount of data available to the RFID system and possiblyincreases the accuracy of the position determination of the RFID tag.The antennas 900 include antennas 900 a, 900 b, 900 c, 900 d, 900 e, 900f and 900 g. The antennas 900 are associated with RFID receivers (notshown); these RFID receivers may be similar to the RFID receivers 114,116 (see FIG. 1), 614, 616 (see FIG. 6), 700 (see FIG. 7), 814, or 816(see FIG. 8). Note that the antennas 900 e, 900 f and 900 g are shownslightly offset, for illustrative clarity.

The antennas 900 may be used in place of one of the sets of antennas ina particular direction. For example, the antennas 900 may be used inplace of the antennas 104 (see FIG. 1) for the x direction, or theantennas 106 (see FIG. 1) for the y direction. The antennas 900 may beused in place of the antennas 604 (see FIG. 6) for the x direction, orthe antennas 606 (see FIG. 6) for the y direction. The antennas 900 maybe used in place of the antennas 804 (see FIG. 8) for the x direction,or the antennas 806 (see FIG. 8) for the y direction.

The antennas 900 may be printed as dual layers on a printed circuitboard. The number, and shape, of the antennas 900 may be adjusted asdesired.

FIG. 10 is an overhead view of an antenna array 1000. The antenna array1000 includes a first set of antennas 1004 a, 1004 b, 1004 c and 1004 d(collectively antennas 1004), and a second set of antennas 1006 a, 1006b, 1006 c, 1006 d, 1006 e, 1006 f, 1006 g, 1006 h, 1006 i (collectivelyantennas 1006). As compared to other of the antenna arrays (e.g., theantennas 104 and 106 of FIG. 1), the antennas 1004 and 1006 do notintersect at right angles. The antenna array 1000 may be used in placeof the antennas 104 and 106 (see FIG. 1), 604 and 606 (see FIG. 6), or804 and 806 (see FIG. 8). The antennas 1004, the antennas 1006, or both,may be overlapping in a manner similar to that of the antennas 900 (seeFIG. 9).

The number, and shape, of the antennas 1004 and 1006 may be adjusted asdesired.

FIG. 11 is an overhead view of a polar antenna array 1100. The polarantenna array 1100 includes overlapping circular antennas 1104 a, 1104b, 1104 c and 1104 d (collectively circular antennas 1104), and radialantennas 1106 a, 1106 b, 1106 c and 1106 d (collectively radial antennas1106). The antennas 1104 are shown with dotted lines. As compared toother of the antenna arrays (e.g., the antennas 104 and 106 of FIG. 1),the antenna array 1100 does not generate x and y position information,but instead generates polar position information (e.g., magnitude anddirection). The circular antennas 1104 are used to determine thedistance from the center point 1110, and the radial antennas 1106 areused to determine the angle. The polar antenna array 1100 may be used inplace of the antennas 104 and 106 (see FIG. 1), 604 and 606 (see FIG.6), 804 and 806 (see FIG. 8), or the antenna array 1000 (see FIG. 10).

As an example, say that the system detects an RFID tag inside of thecircular antenna 1104 d and outside of the circular antenna 1104 c. Ifthe system further detects that RFID tag outside of the radial antenna1106 a, the system determines that the position of the RFID tag is inthe vicinity of the point 1110. The accuracy of the positiondetermination can be determined according to the values of the signalsdetected, as discussed above regarding FIGS. 3-4 (or as further detailedbelow in the section Determining the Positions).

As an option, the circular antennas 1104 need not be overlapping.Similarly, the radial antennas 1106 need not be overlapping. As anotheroption, the circular antennas 1104 can be annular or ring-shaped, andoverlapping or non-overlapping or partially overlapping.

FIG. 12A is an overhead view of a Baccarat table 1200, and FIG. 12B isan overhead view of a portion of the Baccarat table 1200 showing acorresponding portion of an antenna array 1202. In FIG. 12A, the entireantenna array 1202 is present, but not shown. In FIG. 12B, the antennaarray 1202 includes a first set of antennas 1204 a, 1204 b, 1204 c, 1204d, 1204 e, 1204 f, 1204 g and 1204 h (collectively antennas 1204) and asecond set of antennas 1206 a, 1206 b, 1206 c and 1206 d (collectivelyantennas 1206). The Baccarat table 1200 also includes one or more mainantennas (not shown), similar to the main antenna 102 (see FIG. 1). Forone main antenna, it may surround the entire playing area of theBaccarat table 1200. For two main antennas, each may cover a portion ofthe Baccarat table 1200. For example, one may surround the bettingpositions on the left-hand portion of the Baccarat table 1200 (positions7-12), and the other may surround the betting positions on theright-hand portion of the Baccarat table 1200 (positions 1-6).Alternatively, the main antenna can define a bounded area for some (orall) of a single type of bet (e.g. player or banker). Such an array canbe used to track individual bets within the bounded area.

The antennas 1204 and 1206 (and the main antenna) are connected to RFIDreaders (not shown), in a manner similar to the RFID receivers 114 or116 (see FIG. 1). The antennas 1204 are wider at one end than at theother end. The antennas 1206 are slightly bent or curved, in order toconform to the Baccarat table 1200.

As an option, the antennas 1204, the antennas 1206, or both may beoverlapping in a manner similar to that of the antennas 900 (see FIG.9).

FIG. 13 is an overhead view of a roulette table 1300 having an antennaarray 1302. The antenna array 1302 includes a first set of antennas 1304a, 1304 b, 1304 c, 1304 d and 1304 e (collectively antennas 1304) and asecond set of antennas 1306 a, 1306 b, 1306 c, 1306 d, 1306 e, 1306 f,1306 g, 1306 h, 1306 i, 1306 j, 1306 k, 1306 l, 1306 m and 1306 n(collectively antennas 1306). The roulette table 1300 also includes amain antenna (not shown), similar to the main antenna 102 (see FIG. 1),that surrounds the playing area. The antennas 1304 and 1306 (and themain antenna) are connected to RFID readers (not shown), in a mannersimilar to the RFID receivers 114 or 116 (see FIG. 1).

As an option, the antennas 1304, the antennas 1306, or both may beoverlapping in a manner similar to that of the antennas 900 (see FIG.9).

Finally, regarding the sizing of the antennas discussed herein,generally the width of each antenna should be less than the diameter ofthe RFID tags (or within around +/−0.5 inches of the diameter of theRFID tags), and the spacing between each antenna should also be lessthan the diameter of the RFID tags.

Reading the RFID Tags

As discussed above, the RFID reader (e.g., the RFID transmitter 108 ofFIG. 1) sends an inventory command (e.g., 202 in FIG. 2) that the RFIDtags respond to (e.g., 204 in FIG. 2). The RFID tags includeanti-collision features to mitigate interference resulting when two ormore RFID tags respond at the same time. One anti-collision feature is apseudo-random selection of the slot in which they respond.Statistically, the different pseudo-random slots among a plurality ofRFID tags helps prevent them from all responding at the same time.

Another anti-collision feature is the 5 bit CRC that is added to theinventory command which is sent from the tag to the reader along withthe 16 bit CRC of the serial number of the tag. If the CRCs are notcorrect then there is likely a collision. When all the RFID tags havebeen read, the RFID reader stops radiating energy, which causes the RFIDtags to clear their flags; with the cleared flags, the RFID tags arefree to respond when the RFID reader begins radiating energy again whensending the next inventory command.

The RFID reader may implement a slotted Aloha system or a binary treesearch. In the slotted Aloha system, the RFID reader broadcasts aninitialization command and a parameter that the tags individually use topseudo-randomly delay their responses. In the binary tree search, theRFID reader sends an initialization symbol and then transmits one bit ofidentification data at a time; only RFID tags with matching bitsrespond, and eventually only one RFID tag matches the completeidentification string.

Each RFID tag may include 96 bits of identification information, whichallows for 2{circumflex over ( )}96 total RFID tags to be individuallyidentified by the system. The RFID tags may send their responses usingManchester encoding of their modulation on the carrier signal from theRFID reader.

As a result of the anti-collision features, the system can generallyoperate as if only one RFID tag is responding at a given time. Thisallows all of the receivers (e.g., the receivers 112, 114 and 116 ofFIG. 1) that receive a response at a given time to associate togetherthe respective responses received by each receiver. For clarity ofillustration, the remainder of this document assumes that only one RFIDtag is responding at a given time.

Determining the Positions

As discussed above, at least three receivers (e.g., the receiver 112, atleast one of the receivers 114, and at least one of the receivers 116 ofFIG. 1) of the RFID system (e.g., the RFID system 100) receive theresponse from a given RFID tag. For a given antenna in the x direction(e.g., the antenna 104 b), the RFID system can determine that the givenRFID tag is inside of, or outside of, the given antenna by comparing thesignal phases between the given antenna in the x direction and the mainantenna (e.g., the main antenna 102). Similarly, for a given antenna inthe y direction (e.g., the antenna 106 b), the RFID system can determinethat the given RFID tag is inside of, or outside of, the given antennaby comparing the signal phases between the given antenna in the ydirection and the main antenna. When the RFID system determines that thegiven RFID tag is inside of both the x direction antenna and the ydirection antenna, the RFID system determines the position of the givenRFID tag on the gaming table as being at the position where those twoantennas intersect. In a simple case, the RFID system assumes theposition is at the midpoint of the intersection.

When the RFID system determines that the given RFID tag is outside ofeither the x direction antenna or the y direction antenna, the RFIDsystem needs to determine which direction outside. As an example in thex direction, if the given RFID tag is detected outside of the antenna104 b, the given RFID tag may be to the left of, or the right of, theantenna 104 b. At this point, the RFID system looks at the responsesreceived by the antennas adjacent to the antenna 104 b (e.g., theantennas 104 a and 104 c). If the antenna 104 a received the responseand the antenna 104 c did not, then the RFID system determines theposition of the given RFID tag as to the left of the antenna 104 b.Similarly, if the antenna 104 c received the response and the antenna104 a did not, then the RFID system determines the position of the givenRFID tag as to the right of the antenna 104 b. In a simple case, theRFID system assumes the position is at the midpoint between the twoantennas (104 b and 104 a, or 104 b and 104 b). In the y direction, asimilar result occurs.

Interpolation

Instead of assuming the position at the midpoint, as discussed above,the RFID system (e.g., the RFID system 100 of FIG. 1) may interpolatethe position based on the amplitude of the received signal. For example,the RFID system may store the plot 300 of FIG. 3 as a lookup table(e.g., in the controller 120). TABLE 1 is an example lookup table with 7entries, corresponding to 7 segments of the plot 300 (where segment 1 isfrom point 302 down to the maximum negative value of the plot 300;segment 2 is from that point up to point 304; segment 3 is from point304 up to near the maximum positive value of the plot 300; segment 4 isthe portion around the maximum positive value; segment 5 is from nearthe maximum value down to point 308; segment 6 is from point 308 down tothe maximum negative value of the plot 300; and segment 7 is from themaximum negative value up to point 310):

TABLE 1 Segment Amplitude Position 1 From 0 to −0.25 0.5 (approx. point320) 2 From −0.25 to 0 1.4 (approx. point 322) 3 From 0 to 0.7 1.9 4Above 0.7 2.5 5 From 0.7 to 0 3.2 6 From 0 to −0.25 3.75 (approx. point324)  7 From −0.25 to 0 4.2 (approx. point 326)

(Since the plot 300 is symmetric, the data in TABLE 1 may be reduced to4 entries, as offsets around a center point.) As discussed above, theremay be multiple points for a given amplitude detected by a singleantenna, so the RFID system uses adjacent antennas in order to eliminatethe unlikely points.

The position data in TABLE 1 corresponds to the midpoint of each segmentof the plot 300. Instead of using the midpoint when the amplitude fallsanywhere within the appropriate range, the RFID system can interpolateusing the exact amplitude. For example, if the amplitude is at −0.125and (using adjacent antennas) the position is determined to be withinthe first segment, instead of using 0.5 as the position, the RFID systeminterpolates the position as halfway to 0.5, which is 0.25. The RFIDsystem may use linear interpolation.

The number of entries in the lookup table may be increased, ordecreased, as desired. As more entries appear in the lookup table, theinterpolation becomes more accurate to the actual position.

In general, the values in TABLE 1 are applicable to the uniform-widthantennas, such as in FIG. 5. For other antennas, such as the radialantennas 1106 of FIG. 11, or the antennas of FIG. 12B, the values in thecorresponding lookup tables may be determined empirically.

Integration with Game Rules

The RFID system (e.g., the RFID system 100 of FIG. 1) may use thedetermined RFID information (e.g., the detected RFID tag identifiers andpositions) to control various events in the gaming environment. Ingeneral, these events are managed according to game rules, and differentgame rules apply in different gaming circumstances (referred to as gamestates). When the RFID system detects a violation of the game rules, theRFID system may generate an alert. The RFID system may use the RFIDreaders described herein to determine the detected RFID tag identifiersand positions (generally referred to as chip data), and may use aninstrumented card shoe to determine the values of cards dealt (generallyreferred to as card data).

In general, the game states are tailored to a particular game. Forexample, Baccarat may have the following game states: pre-game, newgame, bets locked, payout, and end of game. In the pre-game state, theRFID system is not monitoring RFID tag identifiers or locations. In thenew game state, the RFID system may track RFID tag identifiers andlocations (and may display and record the resulting data), but since thegame rules allow chips to be freely moved around in this state, noillegal move alerts are generated. (An exception may be made fordetecting an illegal chip, which may result an illegal chip alert.) Inthe bets locked state, chip movements are not allowed, so any RFID tagmovements detected may result in an alert. In the payout state, the RFIDsystem monitors that the correct payout amounts are made to the correctlocations, and that the correct collections are made from the correctlocations, by correlating the RFID tags placed at (or removed from) thevarious locations. In the end of game state, the RFID system logs theend of the current game, and returns to the new game state for the nextgame.

A particular game state may include one or more sub-states (that mayalso be referred to as game states). For example, in blackjack, thedealer is obligated to deal another card to the dealer's hand dependingupon the point total of the dealer's hand (e.g., 17). So within the gamestate of “deal cards to dealer's hand”, there is a sub-state of “dealanother card” and a sub-state of “deal no more cards”. Similar statesand sub-states exist for each hand. Similarly, if the dealer is dealt aninitial Blackjack, the RFID system may transition from the “deal” stateto the “collection/payout” state. As another example, Baccarat has avariety of sub-states within the gameplay state that each play positiontransitions between, depending upon the cards dealt. For example, thetransition from play to payout can be staggered for each player.

The RFID system is particularly helpful during the collection and payoutstates. For example, the RFID system determines that Location 1 is awinner, and Location 2 is a loser, based on the game results. The RFIDsystem knows the identifiers of the RFID tags associated with thelocations, and verifies that additional chips corresponding to a correctpayout are made to Location 1, and that the chips associated withLocation 2 are collected.

Further information regarding the game rules and game states can befound in U.S. Application Pub. No. 2015/0312517 and U.S. ApplicationPub. No. 2016/0217645, which are incorporated herein by reference.

Grouping

The RFID system (e.g., the RFID system 100 of FIG. 1) may associate RFIDtags that have similar positions into a single group. (These similarpositions refer to the x-y plane; e.g., two RFID tags stacked on top ofeach other will have similar x-y positions but different z positions.)For example, if the determined positions of two RFID tags are less thanapproximately 0.75× diameters, the RFID system may consider those twoRFID tags to be associated in a group. For example, for RFID tags havinga diameter of 1.5 inches, a group results when two RFID tags are withinabout 1.125 inches. Similar groups may be formed from adjacent stacks ofRFID tags. The controller may then consider that group of RFID tags as asingle unit. For example, instead of interpreting a first RFID tag and anearby second RFID tag as two separate bets (e.g., $100 and $200), thecontroller groups the two RFID tags as a single bet (e.g., $300).Generally, the RFID system may consider a set of RFID tags to be a groupwhen the position of each RFID tag in the set is within a defined range(e.g., 0.75× diameters) of at least one other RFID tag in the set. Forexample, a “stack” of RFID tags will have similar positions (e.g., muchless than 0.75× diameters), so the RFID system determines that stack tobe a group. As another example, a “mound” of RFID tags may havepositions that in the aggregate that are beyond the defined range, butas long as each RFID tag in the mound is within the defined range of atleast one other RFID tag in the mound, the RFID system determines thatmound to be a group.

Grouping may also be used in combination with the game rules (e.g., thegame states and sub-states). For example, in Blackjack, a player isallowed to “double down” (to double the amount of the initial bet) incertain circumstances. In such a situation, the RFID system first usesthe card data to determine that the double down is allowed. Second, theRFID system uses the RFID data to verify that an accurate doubled bethas been placed as a group with the initial bet. (The RFID system maydetermine the initial bet to be a first group and the doubled bet to bea second group.) Third, the RFID system uses the card data to determineif the player's hand is a winner or a loser; for a winner, the RFIDsystem uses the chip data to verify that correct payouts have beenplaced as additional groups with the initial bet and the doubled bet;and for a loser, the RFID system uses the chip data to verify that allthe groups (the initial bet and the doubled bet) are collected. If anyof the data indicates a violation of the game rules, the RFID system maygenerate an alert.

The defined range that the RFID system uses to determine a group may beadjusted as desired. For example, when the defined range is 1.5×diameters, the RFID system determines that two adjacent stacks are agroup.

FIG. 14 is an overhead view of the antennas 104 and 106 of FIG. 1. Ascompared to FIG. 5, FIG. 14 includes 5 RFID tags 1402, 1404, 1406, 1408and 1410. Assume that each RFID tag takes 10 milliseconds (ms) torespond. Assuming no collisions, the read cycle takes 50 ms (10 ms perRFID tag): During this time, the main antenna (not shown) is energized,and the RFID reader connected to the antenna 104 a receives theresponses from the RFID tags 1402 and 1404; the RFID reader connected tothe antenna 104 b receives the responses from the RFID tags 1402, 1404and 1406; the RFID reader connected to the antenna 104 c receives theresponses from the RFID tags 1406, 1408 and 1410; and the RFID readerconnected to the antenna 104 d receives the responses from the RFID tags1408 and 1410. (These responses correspond to the “second set ofresponses” discussed above, at 208 in FIG. 2.) During the same time, theRFID reader connected to the antenna 106 a receives the responses fromthe RFID tags 1402 and 1408; the RFID reader connected to the antenna106 b receives the responses from the RFID tags 1402, 1406 and 1408; theRFID reader connected to the antenna 106 c receives the responses fromthe RFID tags 1404, 1406 and 1410; and the RFID reader connected to theantenna 106 d receives the responses from the RFID tags 1404 and 1410.(These responses correspond to the “third set of responses” discussedabove, at 210 in FIG. 2.)

Compare the above to a system that energizes each antenna separately(e.g., without a main antenna). In such a system, the RFID readerconnected to the antenna 104 a takes 20 ms to perform a read (10 ms foreach of the RFID tags 1402 and 1404), the RFID reader connected to theantenna 104 b takes 30 ms to perform a read (10 ms for each of the RFIDtags 1402, 1404 and 1406), the RFID reader connected to the antenna 104c takes 30 ms to perform a read (10 ms for each of the RFID tags 1406,1408 and 1410), and the RFID reader connected to the antenna 104 d takes20 ms to perform a read (10 ms for each of the RFID tags 1408 and 1410);so reading the x direction takes 100 ms (20+30+30+20). Similarly,reading the y direction also takes 100 ms, for a total read time of 200ms. This is significantly more than the 50 ms discussed above.

Thus, the RFID systems described herein result in a notable improvementin read times as compared to existing systems that energize each antennaseparately.

The above description illustrates various embodiments of the presentinvention along with examples of how aspects of the present inventionmay be implemented. The above examples and embodiments should not bedeemed to be the only embodiments, and are presented to illustrate theflexibility and advantages of the present invention as defined by thefollowing claims. Based on the above disclosure and the followingclaims, other arrangements, embodiments, implementations and equivalentswill be evident to those skilled in the art and may be employed withoutdeparting from the spirit and scope of the invention as defined by theclaims.

What is claimed is:
 1. A system for determining locations of objects ina gaming environment, the system comprising: a main antenna associatedwith an area on a gaming table; a first plurality of antennas orientedin a first direction and associated with the area on the gaming table; asecond plurality of antennas oriented in a second direction, wherein thesecond direction differs from the first direction, wherein the secondplurality of antennas overlaps the first plurality of antennas, andwherein the first plurality of antennas and the second plurality ofantennas intersect at a plurality of locations within the area; a mainradio frequency identification (RFID) transmitter coupled to the mainantenna; an RFID receiver; and a controller that controls the main RFIDtransmitter to generate an RFID inventory command, wherein each of aplurality of RFID tags in the area responds to the RFID inventorycommand according to an anti-collision process, wherein in response tothe RFID inventory command, the RFID receiver receives a first pluralityof responses from the plurality of RFID tags via the first plurality ofantennas and a second plurality of responses from the plurality of RFIDtags via the second plurality of antennas, wherein the controllerdetermines an identifier for each of the plurality of RFID tags using atleast one of the first plurality of responses and the second pluralityof responses, and wherein the controller determines a position of eachof the plurality of RFID tags by correlating phase information of thefirst plurality of responses, and phase information of the secondplurality of responses.
 2. The system of claim 1, wherein in response tothe RFID inventory command, the RFID receiver receives a third pluralityof responses from the plurality of RFID tags via the main antenna, andwherein the controller determines the position of each of the pluralityof RFID tags by correlating the phase information of the first pluralityof responses, the phase information of the second plurality ofresponses, and phase information of the third plurality of responses. 3.The system of claim 2, wherein the controller uses the phase informationof the third plurality of responses to determine relative phaseinformation for the first plurality of responses and relative phaseinformation for the second plurality of responses, wherein thecontroller determines the position of each of the plurality of RFID tagsby correlating the relative phase information of the first plurality ofresponses and the relative phase information of the second plurality ofresponses.
 4. The system of claim 1, wherein the controller determinesthe position of each of the plurality of RFID tags by correlatingamplitude information and the phase information of the first pluralityof responses, and the phase information of the second plurality ofresponses.
 5. The system of claim 1, wherein in response to the RFIDinventory command, the RFID receiver receives a third plurality ofresponses from the plurality of RFID tags via the main antenna, andwherein the controller determines the position of each of the pluralityof RFID tags by correlating amplitude information and the phaseinformation of the first plurality of responses, the phase informationof the second plurality of responses, and the phase information of thethird plurality of responses.
 6. The system of claim 1, wherein for aparticular RFID tag of the plurality of RFID tags, the controllersimultaneously determines the identifier and the position of theparticular RFID tag.
 7. The system of claim 1, wherein the RFIDinventory command is a single RFID inventory command that results in thecontroller determining the identifiers and the positions of all theplurality of RFID tags.
 8. The system of claim 1, wherein the firstplurality of antennas and the second plurality of antennas areoverlapping and intersecting to define the position of each of theplurality of RFID tags in two dimensions within the area.
 9. The systemof claim 1, wherein the first plurality of antennas and the secondplurality of antennas intersect orthogonally and define the position ofeach of the plurality of RFID tags in an x dimension and a y dimensionwithin the area.
 10. The system of claim 1, wherein the first pluralityof antennas and the second plurality of antennas define the position ofeach of the plurality of RFID tags using polar coordinates within thearea.
 11. A method of determining locations of objects in a gamingenvironment, the method comprising: generating, by a main radiofrequency identification (RFID) transmitter coupled to a main antenna,an RFID inventory command, wherein the main antenna is associated withan area on a gaming table; responding, by each of a plurality of RFIDtags in the area, to the RFID inventory command according to ananti-collision process; receiving, by an RFID receiver, a firstplurality responses from the plurality of RFID tags via a firstplurality of antennas in response to the RFID inventory command, whereinthe first plurality of antennas is oriented in a first direction and isassociated with the area on the gaming table; receiving, by the RFIDreceiver, a second plurality of responses from the plurality of RFIDtags via a second plurality of antennas in response to the RFIDinventory command, wherein the second plurality of antennas is orientedin a second direction that differs from the first direction, wherein thesecond plurality of antennas overlaps the first plurality of antennas,and wherein the first plurality of antennas and the second plurality ofantennas intersect at a plurality of locations within the area;determining, by a controller, an identifier for each of the plurality ofRFID tags using at least one of the first plurality of responses and thesecond plurality of responses; and determining, by the controller, aposition of each of the plurality of RFID tags by correlating phaseinformation of the first plurality of responses, and phase informationof the second plurality of responses.
 12. The method of claim 11,further comprising: receiving, by the RFID receiver, a third pluralityof responses from the plurality of RFID tags via the main antenna inresponse to the RFID inventory command, wherein the step of determiningthe position of each of the plurality of RFID tags comprisesdetermining, by the controller, the position of each of the plurality ofRFID tags by correlating the phase information of the first plurality ofresponses, the phase information of the second plurality of responses,and phase information of the third plurality of responses.
 13. Themethod of claim 12, further comprising: determining, by the controller,relative phase information for the first plurality of responses andrelative phase information for the second plurality of responses byusing the phase information of the third plurality of responses, whereinthe step of determining the position of each of the plurality of RFIDtags comprises determining, by the controller, the position of each ofthe plurality of RFID tags by correlating the relative phase informationof the first plurality of responses and the relative phase informationof the second plurality of responses.
 14. The method of claim 11,wherein the step of determining the position of each of the plurality ofRFID tags comprises determining, by the controller, the position of eachof the plurality of RFID tags by correlating amplitude information andthe phase information of the first plurality of responses, and the phaseinformation of the second plurality of responses.
 15. The method ofclaim 11, further comprising: receiving, by the RFID receiver, a thirdplurality of responses from the plurality of RFID tags via the mainantenna in response to the RFID inventory command, wherein the step ofdetermining the position of each of the plurality of RFID tags comprisesdetermining, by the controller, the position of each of the plurality ofRFID tags by correlating amplitude information and the phase informationof the first plurality of responses, the phase information of the secondplurality of responses, and the phase information of the third pluralityof responses.
 16. The method of claim 11, wherein for a particular RFIDtag of the plurality of RFID tags, the step of determining theidentifier for the particular tag is performed simultaneously with thestep of determining the position of the particular RFID tag.
 17. Themethod of claim 11, wherein the RFID inventory command is a single RFIDinventory command, and wherein the steps of determining the identifierand determining the position for each of the plurality of RFID tagsresults in determining a plurality of identifiers and a plurality ofpositions for all of the plurality of RFID tags.
 18. The method of claim11, wherein the first plurality of antennas and the second plurality ofantennas are overlapping and intersecting to define the position of eachof the plurality of RFID tags in two dimensions within the area.
 19. Themethod of claim 11, wherein the first plurality of antennas and thesecond plurality of antennas intersect orthogonally and define theposition of each of the plurality of RFID tags in an x dimension and a ydimension within the area.
 20. The method of claim 11, wherein the firstplurality of antennas and the second plurality of antennas define theposition of each of the plurality of RFID tags using polar coordinateswithin the area.